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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        ! function() {
            var a = 3;
            var c = 9;
            var d = undefined;
            a = (11 <= a);
            console.log(a); // false
            a = (a <= 20);
            console.log(a); // true
            console.log(c - d); // NaN
            console.log('-----------------------');
        }();
        ~ function() {
            var 吴超 = 'tiancai';
            console.log(吴超);
            console.log(parseFloat(true)); // NaN
            console.log(parseFloat(null)); // NaN
            console.log(parseFloat(undefined)); // NaN
            console.log('-------------------------');
            console.log(-null, -'null') // -0 , NaN
            var i = NaN;
            var j = NaN;
            console.log('--------------------------');
            console.log(typeof i == typeof j); //true
            console.log(i == j); //false
            console.log(isNaN(i)); //true
        }();
    </script>
</body>

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